Notes for AKT-090910-1/0:29:24

Invariance of tricolourability under R2. For each of the 2 directions (as in the proof for R1), there are cases (corresponding to different colourings of, say the top, 'external endpoints' of the local diagram modulo colour permutations; the colouring of all arcs will then be forced by the local rule of tricolourability and the fact that we are only dealing with three colours, and the cases which violate the global rule should be discarded) to check.

Terminology (for the purpose of this annotation)
Local rule: at each crossing, of the 3 arcs involved, either 1 or all 3 colours appear.
Global rule: all three colours must appear.